An organic electroluminescence (electroluminescence will be referred to as EL, hereinafter) is a spontaneous light emitting device which utilizes the principle that a fluorescent substance emits light by energy of recombination of holes injected from an anode and electrons injected from a cathode when an electric field is applied.
Since an organic EL device of the laminate type driven under a low electric voltage was reported by C. W. Tang of Eastman Kodak Company (C. W. Tang and S. A. Vanslyke, Applied Physics Letters, Volume 51, Pages 913, 1987), many studies have been conducted on organic EL devices using organic materials as the constituting materials. Tang et al. used a laminate structure using tris(8-hydroxyquinolinol)aluminum for the light emitting layer and a triphenyldiamine derivative for the hole transporting layer. Advantages of the laminate structure are that the efficiency of hole injection into the light emitting layer can be increased, that the efficiency of forming excitons which are formed by blocking and recombining electrons injected from the cathode can be increased, and that excitons formed within the light emitting layer can be enclosed. As the structure of the organic EL device, a two-layered structure having a hole transporting (injecting) layer and an electron transporting and light emitting layer and a three-layered structure having a hole transporting (injecting) layer, a light emitting layer and an electron transporting (injecting) layer are well known. To increase the efficiency of recombination of injected holes and electrons in the devices of the laminate type, the structure of the device and the process for forming the device have been studied.
As the light emitting material, chelate complexes such as tris(8-quinolinolato)aluminum, coumarine derivatives, tetraphenyl-butadiene derivatives, bisstyrylarylene derivatives and oxadiazole derivatives are known. It is reported that light in the visible region ranging from blue light to red light can be obtained by using these light emitting materials, and development of a device exhibiting color images is expected (For example, Japanese, Patent Application Laid-Open Nos. Heisei 8(1996)-239655, Heisei 7(1995)-138561 and Heisei 3(1991)-200889.
Devices using anthracene derivatives as the hole transporting material or the light emitting material are disclosed in Japanese Patent No. 3175816. However, although an excellent device emitting blue light can be made by using the anthracene derivatives, an ink in which the anthracene derivatives are dissolved cannot be prepared since the used compounds are not easily soluble in solvents. The device cannot be produced in accordance with a wet process such as the spin coating process, the printing process and the ink-jet process and is produced in accordance with the vacuum vapor deposition process. Therefore, a compound which can be easily formed into a film in accordance with a wet process, which does not require vacuum, and a device using the compound have been desired.
On the other hand, in Japanese Patent Application Laid-Open No. 2000-143569, a distyryl compound having a soluble substituent is disclosed. However, this compound has a poor light emitting property since this compound does not have the anthracene nucleus or the fluorene nucleus as the central group, and the improvement has been desired.